In the first two days of the campaign, the raids of May 1939 killed more than five thousand Chinese civilians. Two months later, after tens of thousands of deaths, in retaliation for firebombing, the United States embargoed the export of airplane parts to Japan, thus imposing its first economic sanction against that nation. On 5 June 1941, the Japanese flew more than 20 sorties, bombing the city for three hours. About 4,000 residents who hid in a tunnel were asphyxiated. The majority of the air raids conducted against Chongqing were made with squadrons of medium-heavy bombers composed of Mitsubishi G3Ms, known under Allied codename as "Nells", Ki-21s "Sallys", Fiat BR.20 Cicognas, and Kawasaki Ki-48 "Lilys", although towards the end of the war, Mitsubishi G4M "Bettys", Ki-67 "Peggys", Nakajima Ki-49 "Helens", and Yokosuka P1Y "Frances" were also deployed. Due to severe attrition of aircraft and veteran pilots of the Chinese Air Force initially equipped at the outbreak of the air war in 1937 with largely US-made aircraft and training, the Chinese Air Force increasingly relied on the Soviet Union's assistance during the retreat and defense of Wuhan in 1938 and further retreat and defense of Chongqing in 1939–41; Chinese pilots flying primarily the Polikarpov I-16 and I-15 series of fighter-pursuit aircraft in defense of Chongqing and Chengdu. The introduction of the Zero-sen fighter plane in 1940, the most advanced production fighter aircraft at the time, ensured the Japanese practically total air supremacy. Following the Japanese attack on Pearl Harbor in December 1941, the United States declared war on Japan, reinvigorating support for China against Japanese imperialist aggressions, and an immediate Sino-US cooperation with planning of the Doolittle Raid against Japan in April 1942. By August 1943, modern interceptor aircraft possessing greater speed and firepower, ground-based radar equipment, and better aircrew training supplied by the US and other Allied nations left the ROCAF in a much better position to fight back and, along with the diversion of Japanese aerial assets in support of the war in the Pacific, helped curtail further Japanese bombing sorties. The last recorded air raid of the campaign took place on 19 December 1944.
Total bomb tonnage and raids
Three-thousand tons of bombs were dropped on the city between 1939 and 1942. According to photographer Carl Mydans, the spring 1941 bombings were at the time "the most destructive shelling ever made on a city", although terror bombing grew rapidly during the Second World War: by comparison 2,300 tons of bombs were dropped by Allied bombers on Berlin in a single night during the Battle of Berlin. A total of 268 air raids were conducted against Chongqing.
Lawsuit against the Japanese government
In March 2006, 40 Chinese who were wounded or lost family members during the bombings sued the Japanese government, demanding 10,000,000 yen each, and asked for apologies. "By filing a lawsuit, we want the Japanese people to know about Chongqing bombings," said a victim.
